1. Field of the Invention
The present invention relates to an ink jet printing apparatus that performs a printing operation on a print medium while reciprocating a print head that ejects ink.
2. Description of the Related Art
An ink jet printing apparatus can print not only paper and OHP sheets but also various print media such as clothes, cardboards, earthenware, and metal. The ink jet printing apparatus can also print not only print media with flat print surfaces but also print media with protrusions and recesses, curved surface portions, edge portions. The ink jet printing apparatus can also inexpensively print high-quality color images by using a plurality of color inks and a print head that ejects the color inks. In particular, what is called a serial printing apparatus, which enables a reduction in the size and costs thereof, is commonly used; the serial printing apparatus reciprocates a print head along a width direction (main scanning direction) of the print medium, while intermittently conveying the print medium in synchronism with the main scanning.
Current ink jet printing apparatuses perform what is called marginless printing in which the entire print medium is printed without forming a non-printing area (blank) at edge portions of the print medium as is the case with silver halide photography. One method for achieving the marginless printing ejects ink to areas outside the print medium (Japanese Patent Laid-Open Nos. 2004-181826 and 10-315444). An alternative method prints an image on the print medium so as to leave non-printing areas at the edge portions of the print medium and then cuts the leading, trailing, right, and left edge portions of the print medium using a cutting mechanism, thus enabling the marginless printing (Patent Document 3).
The technique disclosed in Japanese Patent Laid-Open Nos. 2004-181826 and 10-315444 enables the marginless printing of standard print media. However, the method disclosed in Japanese Patent Laid-Open Nos. 2004-181826 and 10-315444 is inapplicable to a nonstandard printing apparatus, for example, a printing apparatus configured to print continuous roll paper and to cut the paper into print media using a cutting device provided in the printing apparatus.
In contrast, the technique disclosed in Japanese Patent Laid-Open No. 2001-310513 cuts the non-printing areas using the cutting mechanism provided in the printing apparatus. This eliminates the need for ejection of ink to a platen as required for Japanese Patent Laid-Open Nos. 2004-181826 and 10-315444, thus enabling the marginless printing without contaminating the platen.
In general, with a printing apparatus based on a serial scan method offering a function of cutting print media, if a cutting process is executed during printing, a carriage with the print head mounted thereon is stopped to prevent printing for a given time. If the cutting process is executed between the preceding print scan and the succeeding print scan, the time from completion of printing of an image for the preceding print scan until printing of an image for succeeding print scan is started increases by the time required for the cutting process. For example, in a 2 pass printing method, an image in a predetermined print area is completed by the preceding print scan and the succeeding print scan. Since the cutting process is executed between the preceding print scan and the succeeding print scan, the elapsed time between completion of the preceding print scan and the start of the succeeding print scan increases by the time required for the cutting. During the elapsed time, the ink in a portion of the print medium printed by the preceding print scan dries.
As described above, if the cutting process is executed between the preceding print scan and the succeeding print scan, the time from completion of the preceding print scan until the start of the succeeding print increases compared to a case in which the cutting operation is not performed. This results in a variation in the level of drying of the ink between the two cases. If the level of drying of the ink varies (drying unevenness), the corresponding print area offers a density and a color that are different from those of the other print areas. This may result in printing unevenness, thus degrading printing quality.
On the other hand, if the cutting process is executed when printing of one page is completed on the print medium, the ink drying unevenness as described above does not occur. However, the cutting device needs to be installed downstream of and relatively far from the print head in a conveying direction in order to cut the leading and trailing end portions of the print medium, particularly the leading end portion thereof after the printing of one page has been completed. This increases the size of the printing apparatus.
Thus, Japanese Patent Laid-Open No. 2005-074759 proposes a method of making the adverse effect of the drying unevenness on the printing quality insignificant instead of eliminating the drying unevenness resulting from the cutting process. That is, the time for which the carriage is stopped after each scan (this time is hereinafter referred to as wait time) is varied step by step before and after the cutting process, in order to make the adverse effect of the drying unevenness insignificant. Thus, the drying unevenness is allowed to occur step by step in predetermined ranges of print portions corresponding to the print scans before and after the cutting process, to make the adverse effect of the drying unevenness on the printing quality insignificant.
However, the technique disclosed in Japanese Patent Laid-Open No. 2005-074759 always varies the wait time step by step at a given rate regardless of the amount of ink ejected to the print medium, the type of the ink, and the like. Thus, sufficient printing quality or an appropriate print speed disadvantageously fails to be achieved depending on the type of the image to be printed or the ink used. That is, easiness with which the ink ejected to the print medium dries (this is hereinafter referred to as drying characteristics) varies depending on the type of the ink or the amount of ink applied to the print medium.
For example, if only a small mount of ink is applied to the print medium, the ink ejected to the print medium dries easily. If a large amount of ink is applied to the print medium, the ink is difficult to dry. However, the technique disclosed in Japanese Patent Laid-Open No. 2005-074759 varies the wait time step by step at the given rate. Thus, according to the technique disclosed in Japanese Patent Laid-Open No. 2005-074759, an excessively long wait time is set for images that dry relatively easily owing to the small amount of applied ink, disadvantageously reducing a print speed. In contrast, if a large amount of ink is applied, the wait time is insufficient, and the succeeding scan is performed in an insufficient dry condition. This prevents sufficient exertion of the effect based on the step-by-step variation of the wait time, that is, the effect of making the drying unevenness insignificant. Moreover, the drying characteristics of the ink ejected to the print medium also vary depending on the type of the ink, for example, the ink color. Thus, the technique in Japanese Patent Laid-Open No. 2005-074759 which varies the wait time step by step at the given rate may fail to achieve sufficient printing quality. This printing quality problem is particularly profound in color printing apparatuses that overlappingly eject a plurality of color inks into the print medium.
In addition to the case of the above-described cutting process, printing is halted if a process of folding the trailing end portion of the print medium, a suction recovery process, or the like is executed. In this case, the drying unevenness may also occur to degrade image quality.